p-nitrophenol Degradation Kinetics and Mass Transfer Study by <i>Ralstonia eutropha</i> as a Whole Cell Biocatalyst

Abstract

In this study, p-nitrophenol (PNP) has been utilized by adapted free R. eutropha to degrade 3–14 mg/L initial concentration of PNP. According to the experiments, the biodegradation is nongrowth and based on data analysis with Lineweaver-Burk plot, the reaction was found to be noncompetitive substrate-inhibitory. By analyzing data and using an enzymes-substrate complex model, which represent R. eutropha as a whole-cell biocatalyst, a theoretical mechanism is corroborated. The mechanism comprises of four reactions with distinct kinetic calculations, i.e. production of extracellular enzymes (referred to as enzyme), enzyme-substrate complex equilibrium (with rate of 42.4 hr−1 and equilibrium constant of 0.0159 mg/L), inhibition of enzyme-substrate complex equilibrium (with deactivation rate of –1.50 L·hr−1·mg−1 and equilibrium constant 24.2 mg/L), and substrate decomposition. In alginate-immobilized R. eutropha, the external mass transfer was found to be negligible, the effectiveness factor and the Thiele modulus were calculated to be 0.595 and 3.673 respectively for initial concentration of PNP at 3 mg/L. Furthermore, the calculated effective diffusion coefficient was 2.01 × 10−7 cm2.s−1. As such, the internal diffusion was found to be rate limiting.